1. Field of the Invention
This invention relates to apparatus for cutting or scoring sheet material, and more particularly to apparatus for scoring sheet material, such as glass sheets or continuous glass ribbons, prior to breaking the sheet along the score line or lines.
2. Description of the Prior Art
A known form of glass scoring apparatus is described in our British patent specification No. 1,323,097, and incorporates a cutter assembly which can be moved towards and away from a glass surface to be scored by means of a double acting pneumatic cylinder and piston. In operation, a load air pressure is applied to the top of the piston which is operatively connected to the cutting tool and urges the cutting tool into engagement with the glass surface which is to be scored. When it is desired to remove the cutting tool from the glass, a pre-set air pressure, greater than the load air pressure, is applied to the underside of the piston, overcoming the scoring pressure and causing the piston to rise and the cutting tool to disengage from the glass.
U.S. patent specification No. 2,556,757 proposed the use of a pneumatically-operated diaphragm device with control of the air pressure applied to the top surface of the diaphragm in dependence on the sensed presence of a glass sheet below the cutting tool, the lower surface of the diaphragm being open to the atmosphere and a weak return spring being used to lift the cutting tool away from the glass surface when the air pressure was cut off. U.S. patent specification No. 2,361,049 proposed the use of a diaphragm with a liquid and a spring applying the operating pressure to its upper surface and a countervailing air pressure applied to its under surface, the air pressure being released by a vent valve opened by a sensing device when a glass sheet appeared beneath the cutting tool. Due to the use of springs, both these prior devices would have had relatively long response times to irregularities in the glass surface. Also they could not have been used to make interrupted scores.
It is now recognised that it is desirable to reduce to a minimum the time of response of the cutting tool to irregularities in the glass surface, so as to avoid discontinuities in the score lines. When it is desired to make interrupted scores, the response time is again important if the scores are to be commenced and terminated at the correct positions.
Two characteristic response times can normally be distinguished in glass cutting or scoring apparatus used to make interrupted scores on a glass surface. One response time is the period between a command signal and the instant at which the cutting tool moves in response to the command signal so as to commence or terminate a score at a required position on the glass surface. This response time is critical when the apparatus is being used to make interrupted scores. The other response time is the period required for the apparatus to respond to irregularities in the glass surface contour so as to adjust the vertical position of the cutting tool to maintain the cutting tool in engagement with the glass surface. This response time is an important feature of apparatus which is used to make either continuous or interrupted scores across sheets of material.
The speed with which the cutting tool can respond to irregularities in the sheet material, or to a command that the tool be removed from or applied to the sheet material when it is desired to interrupt or commence a cutting or scoring operation, is dependent on the inertia of the operating mechanism and of the parts which transmit the movement of the operating mechanism to the cutting tool. The greater the inertia the longer the response time and also the greater the variation in response time in varying conditions of operation.
It has been proposed in U.S. Pat. Nos. 3,756,104 and 3,821,910 to use electromagnetic means for applying the cutting load to the tool in order to cut down the response time, but these electromagnetic means still have substantial inertia and so can not reduce the response times as much as could be desired.